The invention relates to the field of intravascular catheters, and more particularly to a balloon catheter.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient""s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty balloons preferably have high strength for inflation at relatively high pressure, and high flexibility and softness for improved ability to track the tortuous anatomy and cross lesions. The balloon compliance is chosen so that the balloon will have a desired amount of expansion during inflation. Compliant balloons, for example balloons made from materials such as polyethylene, exhibit substantial stretching upon the application of tensile force. Noncompliant balloons, for example balloons made from materials such as PET, exhibit relatively little stretching during inflation, and therefore provide controlled radial growth in response to an increase in inflation pressure within the working pressure range. However, noncompliant balloons generally have relatively low flexibility and softness, so that it has been difficult to provide a low compliant balloon with high flexibility and softness for enhanced trackability.
Therefore, what has been needed is a catheter balloon with relatively low compliance, and with improved ability to track the patient""s vasculature and cross lesions therein. The present invention satisfies these and other needs.
The invention is directed to a balloon catheter having a balloon formed at least in part of a blend of a first polymeric material having a first Shore durometer hardness, and at least one additional polymeric material of essentially the same composition as the first polymeric material but compounded to have a Shore durometer hardness less than the Shore durometer hardness of the first polymeric material. The balloon of the invention has enhanced softness and flexibility due to the presence of the second polymeric material, and a lower than expected compliance. In a presently preferred embodiment, the balloon is formed of a blend of polymeric materials comprising polyether block amides.
In accordance with the invention, the balloon formed from a blend of polymeric materials preferably has a compliance which is not substantially greater than the compliance of a balloon made from 100% of the first polymeric material, e.g. a compliance less than about 20% greater, preferably less than 15% greater, and most preferably less than 10% greater than the compliance of a balloon made from 100% of the higher Shore durometer material. In a preferred embodiment, the compliance of the blend is not greater than the compliance of a balloon formed of 100% of the higher Shore durometer material. Additionally, the polymeric material blend which forms the balloon has a flexural modulus which is less than the flexural modulus of the first polymeric material. The softness and flexibility of a balloon is a function of the flexural modulus of the polymeric material of the balloon, so that a balloon material having a lower Shore durometer hardness, which thus provides a soft and flexible balloon, has a lower flexural modulus. Thus, the balloon of the invention has enhanced softness and flexibility, yet does not have the increased compliance which would be expected from the amount of the second polymeric component having a lower Shore durometer hardness than the first polymeric component.
In one embodiment of the invention, the balloon is semi-compliant or noncompliant. The term xe2x80x9cnoncompliantxe2x80x9d, should be understood to mean a balloon with compliance of not greater than about 0.03 millimeters/atmospheres (mm/atm). The term xe2x80x9csemi-compliantxe2x80x9d should be understood to mean a balloon with a compliance not greater than about 0.045 (mm/atm). In contrast, compliant balloons typically have a compliance of greater than about 0.045 mm/atm.
The first polymeric material may range from about 10 to about 90% of the blend, and the second component of the blend may range from about 90 to about 10%. The blend preferably has an amount of the second polymeric material which is greater than or equal to the amount of the first polymeric material. In a presently preferred embodiment, the balloon is formed of a blend of polyether block amide polymeric materials having different Shore hardness. A suitable polyether block amide copolymer for use in the polymeric blend of the invention is PEBAX, available from Elf Atochem.
The balloon of the invention is formed by extruding a tubular product formed from the blend of the first polymeric component and at least a second polymeric component. In a presently preferred embodiment, the balloon is formed by expanding the extruded tubular product in a balloon mold. Axial tension may be applied to the balloon during expansion, and the balloon may be cooled under pressure and tension between blowing steps. In one embodiment, the balloon is formed by expanding the extruded tubular product in a series of successively larger balloon molds.
Various designs for balloon catheters well known in the art may be used in the catheter system of the invention. For example, conventional over-the-wire balloon catheters for angioplasty or stent delivery usually include a guidewire receiving lumen extending the length of the catheter shaft from a guidewire port in the proximal end of the shaft. Rapid exchange balloon catheters for similar procedures generally include a short guidewire lumen extending to the distal end of the shaft from a guidewire port located distal to the proximal end of the shaft.
The balloon catheter of the invention has improved performance due to the flexibility, softness, and controlled expansion of the balloon. The polymeric blend provides the surprising result of a balloon having relatively low compliance, for controlled balloon expansion, and having relatively high flexibility and softness, for excellent ability to track the patient""s vasculature and cross lesions. These and other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings.